Estimation of thermal contact conductance of spacecraft heat sink bolted joints

Abstract

Efficient thermal management is one of the key steps required to minimize failure and enhance the lifespan of electronic packages deployed in space applications. Precise and accurate knowledge of thermal contact conductance at the electronics package — heat sink interface is a key input required to achieve the efficient design of heat sinks for the mentioned application. In this study, a novel non-intrusive method for estimating the spatially varying thermal contact conductance for thin-plate bolted joints used in spacecraft thermal control systems is presented. A five bolt configuration joining the electronics package base plate to the heat sink plate is considered. Different bolt torques and their effect on the interface thermal contact conductance between the plates are investigated. Using pressure-sensitive films, the actual contact area and its spatial variation is determined for each torque level in the range of 1.5 N m to 9.0 N m and the contact interface is divided into three regions. Heat transfer experiments are carried out in vacuum at a pressure of 1×10−6 mbar for different combinations of bolt torques, heat load and heat sink temperatures. The thermal contact conductance values over the three regions are simultaneously estimated using an inverse parameter estimation technique. To improve the computational accuracy of the estimation process, a two stage stochastic optimization technique using the Monte-Carlo random sampling algorithm is used and the obtained estimates are compared. With an increase in applied bolt torque from 1.5 N m to 6.0 N m, the actual contact area and the area weighted interface thermal contact conductance are found to increase by 72.26% and 138.82%, respectively. Furthermore, the stochastic estimates of the spatially varying thermal contact conductance obtained using the developed methodology are found to follow a normal distribution with the average limit of standard deviation being ±7.34%, ±6.26% and ±13.22% of the mean values for the considered three regions respectively.